The present invention relates generally to the field of magnetic data storage and retrieval systems. In particular, the present invention relates to a method for fabricating a thin film transducing head having improved thermal dissipation properties.
In a magnetic data storage and retrieval system, a thin film transducing head generally includes a transducer, a substrate upon which the transducer is built, and an overcoat deposited over the transducer. The transducer typically includes a writer portion for storing magnetically-encoded information on a magnetic media and a reader portion for retrieving the magnetically-encoded information from the magnetic media. The reader portion typically consists of a bottom shield, a top shield, and a giant magnetoresistive (GMR) sensor positioned between the bottom and top shields.
The writer portion typically consists of a top and a bottom pole, which are separated from each other at an air bearing surface of the writer by a gap layer, and which are connected to each other at a region distal from the air bearing surface by a back gap closer or back via. Positioned between the top and bottom poles are one or more layers of conductive coils encapsulated by insulating layers, or a writer core. The writer portion and the reader portion are often arranged in a merged configuration in which a shared pole serves as both the top shield in the reader portion and the bottom pole in the writer portion.
To write data to the magnetic media, an electrical current is caused to flow through the conductive coils to thereby induce a magnetic field across the write gap between the top and bottom poles. By reversing the polarity of the current through the coils, the polarity of the data written to the magnetic media is also reversed. Because the top pole is generally the trailing pole of the top and bottom poles, the top pole is used to physically write the data to the magnetic media. Accordingly, it is the top pole that defines the track width of the written data. More specifically, the track width is defined by the width of the top pole at the air bearing surface.
During operation of the magnetic data storage and retrieval system, the transducing head is positioned in close proximity to the magnetic media. The distance between the transducer and the media is preferably small enough to allow for writing to and reading from the magnetic media with a large areal density, and great enough to prevent contact between the magnetic media and the transducing head. Performance of the transducer depends primarily upon head-media spacing (HMS). Pole-tip recession/protrusion (PTR) at the air bearing surface is considered to be a primary technical gap for hitting required HMS targets. During high drive ambient temperatures, PTR increases the risk of head-disc contact and the attendant mechanical reliability problems, while during cold write it can increase the HMS to the point of degrading writeablity, signal-to-noise ratio, and bit error rate. Control of the overall PTR performance is critical in magnetic head designs.
The layers of the transducer, which include both metallic and insulating layers, all have different mechanical and chemical properties than the substrate. The differences in properties affect several aspects of the transducer, including pole-tip recession (PTR) of the metallic layers of the transducer with respect to the substrate at an air bearing surface (ABS) of the transducing head. Two components of the PTR effect exist, thermal pole tip recession/protrusion (TPTR) and current-induced recession/protrusion (CPTR). TPTR arises from isothermal (global) temperature changes in the transducing head during drive operation. TPTR is proportional to the difference in coefficients of thermal expansion (ΔCTE) between the transducing head and substrate materials. Many novel proposals have been made to reduce the TPTR magnitude using low CTE materials, reduced metal material volumes, and compensation schemes.
CPTR results from localized joule heating during application of currents to the writer coil and the resultant heat dissipation into the surrounding components of the transducing head. CPTR, in contrast to TPTR, is proportional to first order to the ΔT(CTE) product, where ΔT is the localized temperature rise in the writer core and CTE is that of the core fill material. At large write currents in the writer coil, ΔT can be more than 20° C., causing CPTR to exceed 0.3 μm, which is a large fraction of the total fly height budget. In the drive, heat transfer to the disc will reduce this value by 3–5 times, but it will still be a large portion of the total fly height budget. This drives constraints on write current, which conflict with performance requirements, thus, reducing CPTR must be pursued in parallel with TPTR reduction.
In principle, CPTR can be reduced by improving thermal conduction away from the coil and the surrounding core structure so that the localized temperature rise is diminished. Current writer designs use a combination of baked photoresist and sputtered Al2O3 as core fill materials, both of which have small thermal conductivities. Replacing these materials with other, high-thermal conductivity materials is a theoretically straightforward way to optimize the core for thermal dissipation. However, this is difficult due to a processing requirement of filling the coil structure, which near the ABS has up to 3:1 aspect ratio trenches between the coil turns. Future designs with similar core lengths for efficiency and a larger number of turns for higher magnetomotive force (MMF) may increase the aspect ratio as well. Thus, a need exists for a writer core structure with improved thermal dissipation that is feasible to fabricate.